Pressure washer devices are used to provide high-pressure, heated fluid to a surface to be cleaned. Such high-pressure fluid can include heated water, or a cleaning solution comprised of a mixture of water and detergent, soap, or other chemicals. The high pressure fluid is delivered to a surface or article to be cleaned by a spray gun that typically employs a user-controlled trigger. As is further understood by those skilled in the art, a pump is typically used to continuously pressurize the fluid in the pressure washer device. Pressure washer devices commonly utilize positive displacement pumps that continuously pump fluid through the system, whether the trigger or other mechanism of the spray gun is activated or deactivated. The flow of liquid through the system also typically functions to cool system components, such as the pump. On occasion, such as when the trigger mechanism is not activated, fluid is not allowed to exit the device, even though the device may be in operation. In this condition, the device has a tendency to overheat the cleaning fluid and/or develop unacceptably high system pressures. To avoid those conditions, devices of the prior art employ a bypass system and/or an automatic pump shut down system. However, these systems do not always prevent overheating and often result in unwanted system shut downs. It is thus desirable to provide a pressure washer device that can continuously pump liquid without adversely affecting the operation of or causing damage to the pressure washer device when the trigger of the spray gun assembly is deactivated.
With reference to FIG. 1, pressure washer devices 2 of the prior art typically utilize a positive displacement pump 6 and a power source 10, such as an internal combustion engine, to heat and move fluid through the device 2. Pump 6 is typically interconnected to an inlet conduit 14 and an outlet conduit 18 and transfers the incoming fluid from the inlet conduit 14 to the outlet conduit 18. The outlet conduit 18 is usually connected to a spray gun 22, which has a trigger 94 or other mechanism that when activated, allows pressurized fluid to exit the wand 86 at nozzle 90.
A water supply tank 30 holds the incoming fluid, typically water, and is interconnected to a supply conduit 32. An inlet filter 54 is often located downstream of the water supply tank 30 to remove contamination and debris from fluid pumped out of the water storage tank 30. Additionally, pressure washer 2 accommodates a cleaning solution container 62 or tank that contains a cleaning solution that may be mixed with water supplied by fluid supply tank 30. The cleaning solution may be detergent, soap, or other chemicals to be mixed, in inlet conduit 14, with fluid stored in tank 30. A metering valve 66 is typically placed near or downstream of the cleaning solution container 62 to control the amount of cleaning solution that is mixed with the fluid.
In operation, pumps of pressure washers typically operate continuously, whether the trigger of the spray gun is activated or deactivated, which causes excess pressure to accumulate in the pump 6, pump inlet conduit 14, the pump outlet conduit 18, and associated components of the pressure washer device when the trigger of the spray gun assembly is not activated. To address the accumulation of excess pressure, an unloader bypass valve 74 is typically employed that re-circulates fluid to the pump via a bypass hose 78 that is interconnected to the pump inlet conduit 14 with a three-opening tee fitting 50. As will be appreciated by one of skill in the art, the temperature of the re-circulating fluid will eventually rise (e.g., reach the boiling point of the fluid in about 20 minutes), which can damage the pressure washer components. The excess temperature is typically removed by a thermal relief valve 70. That is, when the temperature of the fluid in the bypass circuit reaches a predetermined level, the thermal relief valve is opened to dispel the heated water, which wastes water/detergent. It is important to note that detergent is not siphoned from the detergent container 62 to the pump inlet conduit 14 when in a bypass mode, as the pressure in the pump inlet conduit 14 is not reduced.
FIG. 2 shows another prior art pressure washer device having similar components of that described above. This device, however, does not generally employ a thermal relief valve. Here, when the trigger 94 of the spray gun 22 is not depressed, the unloader bypass valve 74 directs fluid from the pump outlet conduit 18 to the bypass hose. The bypass hose directs fluid directly to the water supply tank 30. To complete the bypass circuit, fluid is drawn from the water supply tank 30 into the pump inlet conduit 14 and into the pump 6. The system has a drawback of creating a pressure drop associated with depositing water directly into the water supply tank 30 where the water being pulled from the water storage tank 30 by the pump 6 via the pump inlet conduit 14 has a lower pressure which causes detergent to be drawn into the pump inlet conduit 14 from the detergent container 62. As one skilled in the art will appreciate, this system wastes detergent as eventually the fluid in the water supply tank will become saturated with detergent. When the spray gun 22 is actuated, the fluid being deposited thereby will have an often undesirable concentration of detergent.
To address these problems, a number of pressure washers have utilized an unloader bypass valve 74 that is opened when excess pressure accumulates in the pressure washing device. U.S. Pat. No. 5,230,471 to Berfield is such a device, which is incorporated by reference herein, that utilizes a bypass system comprising a valve that regulates the build up of pressure when a spray nozzle is closed. More specifically, fluid is normally directed through an outlet conduit and discharged through the spray nozzle. When the spray nozzle is closed, liquid is continuously pumped at the same pressure level. The build up of pressure is relieved by the valve which directs fluid to flow from the outlet conduit to a bypass conduit 78 and ultimately to the inlet conduit 14 via tee fitting 50. However, Berfield does not address the problem of dangerously high fluid temperature caused by continuous operation of the pump. Though the fluid is allowed to recirculate, no cooler incoming fluid is introduced because the bypass conduit merely redirects the fluid downstream of the fluid tank 30 and thus into pump inlet conduit 14 and towards the pump 6. As will be understood by skilled artisans, this design may cause pump components to overheat, causing the damage to the device or the device to unwontedly shut down.
U.S. Pat. No. 5,979,788 to Rancourt, et al. discloses a further improvement to regulate the pressure and to prevent rapid overheating of a pressure washer system and is incorporated into this disclosure by reference. Rancourt also utilizes a bypass port to recirculate liquid pumped through the pressure washer device when the spray gun or other mechanism is not in use. In particular, when the spray gun is not in use and the pump is continuously operating, fluid flows into an inlet port and through an unloader valve, which directs the fluid out a bypass port. If the temperature of the recirculating fluid exceeds a maximum threshold level, the thermal relief valve opens and discharges the overheated fluid from the system. A separate pressure relief valve is also included to accommodate excess pressure levels in the recirculated fluid. Thus, if pressure levels exceed a maximum threshold level, the pressure relief valve will also open and discharge water from the system. While Rancourt does not depend on a predetermined level of excess pressure to redirect fluid through the bypass port, Rancourt wastes a substantial amount of fluid through the use of thermal relief and pressure relief valves. The activation of the thermal relief valve and the pressure relief valve can also require additional time and thus costs to cleaning tasks due to periods of inoperability of the pressure system that occur when the valves are active. Rancourt also requires the use of numerous additional components to achieve its safety features, increasing manufacturing costs of the overall device substantially.
Furthermore, the prior art pressure washer devices of Berfield or Rancourt do not prevent the siphoning effect alluded to above. Specifically, when a pressure washer device is in bypass mode, i.e. the trigger of the spray gun assembly is deactivated and the pump continues to operate to move fluid through the device, the prior art pressure washer devices often experience a siphoning effect. More specifically, the unloader valve and associated bypass conduit of the prior art direct cleaning solution at such a volume and flow rate that additional detergent is often pulled from the detergent container. When the trigger is depressed, the detergent laden fluid is expelled. As one of skill in the art will appreciate, this undesirable effect wastes detergent and subjects the item being cleaned to excess detergent, solvent, etc., which may be destructive to the item.
Accordingly, there is a long felt need for a pressure washer device with a bypass system that can re-circulate fluid to the water storage tank that also prevents siphoning of cleaning solution into the incoming fluid supply tank. There is also a need for a pressure washer device which recirculates fluid at a lower temperature than currently available to prevent overheating of the pump or other device components when the trigger or other mechanism of the spray gun assembly is not activated.